ca01 only detailed ToC 1..24

1.1.2 Nickel–Allyl Complexes 43
NiCl(py)2
27
OTBDMS
+
Br
DMF
photolysis
72%
34
OTBDMS
(E)-1-(tert-Butyldimethylsiloxy)-4-methylpent-1-ene (33): [38]
A 100-mL Schlenk tube, equipped with a magnetic stirring bar, was sequentially charged
with TBDMSCl (3.56 g, 23.6 mmol, 1.30 equiv), MeCN (30 mL), (MeO)(TMSO)C=CMe 2
(3.69 mL, 18.2 mmol, 1.00 equiv; added as a proton-scavenging reagent), and propenal
(2.43 mL, 36.4 mmol, 2.00 equiv). The mixture was stirred for 5 min, during which time
N 2 was bubbled through the soln. The soln was then transferred via a cannula into a 100mL
Schlenk tube containing [Ni(cod) 2](2; 5.00 g, 18.2 mmol, 1.00 equiv) and a spinning
stirrer bar, followed by an MeCN wash (5 mL) to complete the transfer. The resulting
deep burgundy-red soln was stirred for 1 h and then concentrated under reduced pressure
(0.01 Torr) for 14 h to afford a dark red solid contaminated with cycloocta-1,5-diene. The
solid was dissolved in MeCN (30 mL) and sequentially treated with (MeO)(TMSO)C=CMe 2
(0.10 mL, 0.49 mmol, 0.03 equiv), DMF (14 mL, 182 mmol, 10.0 equiv), and 2-iodopropane
(14.1 mL, 181 mmol, 10.0 equiv). The resulting burgundy-red soln was stirred for 5 min
and then irradiated with sunlight or a 275-W GE Model RSW sunlamp until the burgundy-red
color of the allylnickel complex had been completely discharged (ca. 12 h), during
which time a brown-green crystalline precipitate was deposited and the supernatant became
light blue-green or nearly colorless (depending on the completeness of the precipitation).
The supernatant was transferred via a cannula into a round-bottomed flask containing
pentane, and the cloudy mixture was stirred for 30 min to complete precipitation
of the nickel dihalide coproduct. The supernatant was then transferred through a filter
paper tipped cannula onto a stirred aq KH 2PO 4/NaOH buffer (150 mL, pH 7) (an emulsion
tended to form at this stage if most of the nickel dihalide had not been removed through
the prescribed procedure). The pentane layer was separated, washed with H 2O(3”20mL),
dried (MgSO 4), and concentrated under reduced pressure (15 Torr) to afford the crude
product [(E/Z) 10:1] as a clear, yellow oil, contaminated by cycloocta-1,5-diene and 2-iodopropane.
Column chromatography (silica gel, 343 g, hexane/EtOAc 98:2) afforded pure 33;
yield: 2.64 g (68%); bp 768C/15 Torr; (E/Z) > 40:1.
1-(tert-Butyldimethylsiloxy)-3-vinylcyclopentene (34): [38]
A 100-mL Schlenk tube equipped with a magnetic stirring bar and rubber septum was
charged with [NiCl 2(py) 4] (10.0 g, 22.4 mmol, 1.00 equiv) and evacuated and refilled with
N 2 twice to establish an inert atmosphere. THF (40 mL) was added, followed by cycloocta-
1,5-diene (8.20 mL, 67.2 mmol, 3.00 equiv), and the resulting mixture cooled to 0 8C. A second
100-mL Schlenk tube containing Na metal strips (1.03 g, 44.8mmol, 2.00 equiv; each
ca. 2 cm ” 0.4 cm ” 0.1 cm) was connected to this flask with a flexible adapter (available
from Aldrich) under a rapid flow of N 2 (an inert atmosphere having previously been established
in the second Schlenk tube and adapter by capping the free end of the adapter and
evacuating and refilling with N 2). The Na strips were then transferred to the stirred 0–58C
mixture in four portions over 1.5 h to give, after an additional 40 min at 0–58C, a very
dark brown (but not black) supernatant, a small amount of precipitated yellow [Ni(cod) 2],
and no apparent blue [NiCl 2(py) 4]. The mixture was treated with a soln of cyclopent-2enone
(1.88mL, 22.4 mmol, 1.00 equiv) and TBDMSCl (3.38g, 22.4 mmol, 1.00 equiv) in
THF (15 mL) and stirred at 258C for 30 min to afford an orange mixture. A soln of bromoethene
(4.74 mL, 67.2 mmol, 3.00 equiv) in THF (5 mL) was added via a cannula, and the
mixture was irradiated at 10 8C with a 275-W GE Model RSW sunlamp for 12.5 h to afford
an olive-green precipitate and a light brown supernatant. The mixture was poured into a
2-L separatory funnel containing pentane (400 mL) and aq KH 2PO 4/NaOH buffer (400 mL,
for references see p 79